Monday, January 08, 2007

A National Geographicarticle by Richard A. Lovett reports on "more than 200 human-caused temblors, mostly in the past 60 years," the majority from coal mining.

The most damaging earthquake in Australia's history was caused by humans, new research says.

The magnitude-5.6 quake that struck Newcastle, in New South Wales, on December 28, 1989, killed 13 people, injured 160, and caused 3.5 billion U.S. dollars worth of damage.

That quake was triggered by changes in tectonic forces caused by 200 years of underground coal mining, according to a study by Christian D. Klose of Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York.

The quake wasn't enormous, but Australia isn't generally considered to be seismically active and the city's buildings weren't designed to withstand a temblor of that magnitude, Klose said.

All told, he added, the monetary damage done by the earthquake exceeded the total value of the coal extracted in the area... [emphasis mine]

Three of the biggest human-caused earthquakes of all time, he pointed out, were a trio that occurred in Uzbekistan's Gazli natural gas field between 1976 and 1984. Each of the three had a magnitude greater than 6.8, and the largest had a magnitude of 7.3...

But as far as he knows, mining engineers aren't examining this, because they are currently unaware of the earthquake risk.

The danger is also relevant to proposals to sequester carbon dioxide by injecting it into geologic formations deep underground where the gas cannot escape and contribute to global warming.

"That alters stress in the crust [too]," Klose said, adding that the risk of earthquakes should be taken into account in planning the locations of such facilities...

A carbon-sequestration plan could reduce the risk of some types of damage (such as from hurricanes, which some scientists say are being strengthened by global warming), while increasing the risk of others, like earthquakes.